The container market for bottled water requires not only low levels of acetaldehyde (AA) in the container sidewall but also minimal color. AA is an inherent byproduct which is generated during the polymerization melt phase and subsequent processing steps, and is known to diffuse into the packaged contents leading to an undesirable taste. The amount of residual AA can also be influenced by variables such as catalyst selection in the polymer synthesis. Prior art has demonstrated that blending low levels of polyamide having terminal amino groups with the poly(ethylene terephthalate), PET, can significantly reduce the amount of AA.
In addition to very low levels of residual AA, the industry also demands that the product color be as low as possible. The clarity and bottle sidewall color permits the use of "natural" or colorless water bottles, and also facilitates the intentional addition of dyes to generate desired color bottles.
In spite of significant improvement in reducing the amount of AA available to desorb into the package content, the solution currently available addresses only a part of the problem. The color of the polyester/polyamide blend is still unsatisfactory, particularly when higher amounts of polyamide are required. In fact, bottles produced with a commercial concentrate blended with PET have a yellowish color, which fades with time. The polyamide currently employed in such blends contains a high level of terminal amino groups, which adversely affect the color of the polyester blend.
U.S. Pat. No. 5,258,233 discloses the use of a low molecular weight polyamide/PET blend to reduce acetaldehyde. The patent discloses that less than 2.0 weight percent of the polyamide should be used to minimize color and haze. However even at 0.5 weight percent, undesirable levels of color can be generated.
Similarly, U.S. Pat. No. 5,266,233 discloses that low molecular weight polyamide/PET copolyesters blend reduces acetaldehyde. Again, it is emphasized that 0.05 to 2.0 weight percent of the polyamide be used to effectively reduce acetaldehyde while maintaining color and clarity. However, undesirable levels of color can be generated even when 0.5 weight percent polyamide is blended with PET copolyesters.
U.S. Pat. No. 5,340,884 teaches the art of precompounding the polyamide with polyesters to create a concentrate that can be diluted with a polyester and still yield the desired properties.
U.S. Patent No. 5,650,469 discloses the use of PET manufactured from purified terephthalic acid, PTA, rather than dimethyl terephthalate, DMT, to achieve better color in the final PET/polyamide blend.
In view of the above, the objective of the present invention is to develop the system which yields a product having reduced levels of less AA and improved color. Another object of the invention Is to provide polyester/polyamide blends that exhibit superior color for various applications.